1. Field of the Invention
This invention relates to a tool for extracting broken bolts, screws and the like. More specifically, this invention relates to a single-piece tool adapted to be installed in the chuck of a counter-clockwise rotating drill to extract broken bolts, screws and the like.
2. Description of Related Art including Information Disclosed under .sctn.1.97 to 1.99
The prior art discloses a number of threaded devices for removing broken bolts or studs. For instance, the old Pat. No. 1,105,535 which issued Jul. 28, 1914 to J. O. Roberts discloses merely a steeply pitched left-hand auger bit adapted to be inserted into a hole separately drilled in the broken bolt. The bit is turned counter-clockwise to remove the broken bolt.
Pat. No. 2,062,383 which issued Dec. 1, 1936 to M. A. West discloses a double-ended tool having threads of opposite hand on its respective ends. The reaming and removing end bas a beveled tip and the driving end has a flat tip. Both ends operate in the recess of a special screw.
Pat. No. 2,281,164 which issued Apr. 28, 1942 to H. S. Maling discloses a right-hand threaded sleeve adapted to be screwed into the hole of the broken bolt, the sleeve having a left-hand threaded bore into which a threaded mandrel is screwed, the mandrel having teeth or nibs on its bottom to dig into the bolt remnant so that the remnant is removed as the sleeve is unscrewed.
Pat. No. 2,684,606 which issued Jul. 27, 1954 to J. A. Brawley provides a left-hand self-threading tap adapted to be screwed into a hole drilled into a bit remnant. A locknut is provided to connect integrally the tap and the remnant. The tap is turned to remove the remnant.
A screw extractor in the Berendzen 4,078,458 which issued Mar. 14, 1978 discloses a drill on the end of a tapered threaded cone whereby a hole can be drilled in the remnant and, drilling farther, the cone can engage the margins of the hole to spin the remnant out of its threaded hole.
More recently a number of meritorious patents have issued to Eli Polonsky in which a left-hand drill bit is provided with a gripping fixture on its stem, and adapted to bite into the hole made by the drill so that the remnant may be removed in a single operation as the device is turned counter-clockwise. The Polonsky patents now assigned to my assignee are:
______________________________________ 4,604,917 which issued August 12, 1986 4,777,850 which issued October 18, 1988 5,031,487 which issued July 16, 1991 ______________________________________
Most of the previous extractor techniques involve first drilling a hole into the remnant and then inserting some form of extractor which engages the drilled hole thereby allowing the remnant to be rotated out of its bore.
Problems can arise with this technique. First, by drilling a hole into the broken remnant, the remnant itself is weakened. A sufficient amount of the broken bolt must remain to give the extractor material to grab in order to transmit a rotational force to remove it. Second, the extractor must be able to fit inside the previously drilled hole. This means that the extractor portion that engages the remnant must be smaller than the remnant itself so that it can fit into this drilled hole. Since the extractor must be smaller than the remnant, a potential for breakage of the extractor is high. The most common cause of dissatisfaction with the previous extraction methods is breakage of the tool when attempting an extraction.
Therefore, an optimum tool for extracting broken bolts must
1. drill a hole as small in diameter as possible so as not to break the wall on the screw, PA1 2. have an extractor as large as possible so as not to break the extractor, PA1 3. drill a hole as shallow as possible and still give enough depth to work. Shallowness is a virtue because the broken part is invariably hard and drilling in it takes valuable time of the mechanic.
None of the previous extractors address the importance of keeping the drilled hole as shallow as possible and the extractor as large as possible.
My extractor addresses all of the above requirements. First, it offers a drill that is optimally sized for a particular application, that is, particular size remnant. Second, it offers an extractor that is as strong as possible for the bore drilled by the drill. Third, it is structured to engage a broken bolt with the shallowest hole drilled into the remnant.